JPEG Rotation and EXIF Orientation

http://blog.csdn.net/daisyhd/archive/2010/11/10/6000962.aspx

 

JPEG Rotation and EXIF Orientation

Digital Cameras with orientation sensors allow auto-rotation of portrait images. Unfortunately, support for this feature is not widespread or consistently applied.

Digital Cameras with Orientation Sensors

Many newer digital cameras (both dSLR and Point & Shoot digicams) have a built-in orientation sensor. Virtually all Canon and Nikon digital cameras have an orientation sensor. The output of this sensor is used to set the EXIF orientation flag in the image file's metatdata to reflect the positioning of the camera with respect to the ground. Canon calls their sensor the "Intelligent Orientation" sensor. It is presumably a 2-axis tilt sensor, allowing 4 possible orientations to be detected (shown in the left side of the diagram below). 
EXIF Orientation Flag Values

 

Note that one would only expect the four orientation settings shown on the left to be possible with a digital camera. The other four settings would imply that the resulting image was flipped horizontally before recording. Unless the camera were to encode the image right-to-left or know that you were taking a photo in a mirror, I don't see how these values will ever be used.

The values 1-8 represent the following descriptions (as shown by utilities that support EXIF field decode): EXIF Orientation Value Row #0 is: Column #0 is:
1 Top Left side
2 Top Right side
3 Bottom Right side
4 Bottom Left side
5 Left side Top
6 Right side Top
7 Right side Bottom
8 Left side Bottom

Auto-rotation in Digital Cameras

While your digital camera may include an option to "auto-rotate images" due to the camera's orientation, this is almost always just a "virtual rotation". A flag is set to indicate to the viewing software / LCD preview which way to rotate the image before display, rather than rotating the image content itself.

As lossless image rotation is a fairly compute-intensive operation, digital cameras are not likely to include true lossless rotation after capturing the photo. The CCD/CMOS sensor hardware is designed to stream raw data in a particular direction (e.g. rows then columns), and so it may be hard to incorporate true auto-rotation in-camera without a performance impact to continuous shooting (frames per second).

Software Support for Orientation

While there are countless software programs available today that display JPEG images, only a subset of them actually interpret the EXIF Orientation flag. Just like color management, many programs simply display the JPEG image as it is stored, and completely ignore any extra details stored in the file's metadata. The most important of these additional details is the Orientation flag, stored in the JPEG APP1 marker under EXIF IFD0. Application Orientation Supported?
Windows Picture and Fax Viewer No
IrfanView Yes (need to enable) 
Photoshop  Yes

IrfanView Auto-rotation

In IrfanView, auto-rotation is not enabled by default. To ensure that images are auto-rotated, you will find the option located under Options->Properties in the JPG/PCD/GIF tab.

Windows Picture and Fax Viewer

Surprisingly, the Windows Picture and Fax Viewer (built into Windows XP) does not support the EXIF orientation flag. This is surprising, as the makers have obviously thought enough to support lossless rotation functions. So, what you will see shown by the viewer is the real image data (assuming landscape orientation), without respecting any indication from the camera as to the real orientation of the image.

Beware of Rotating Photos in Windows Picture and Fax Viewer!

Another surprising detail is that if you decide to perform lossless image rotation (by using the Rotate Clockwise or Rotate CounterClockwise buttons), the EXIF Orientation flag is removed! As the flag is removed, if you do a double-rotation on a portrait photo (rotate, then rotate in the opposite direction), the resulting orientation observed by other viewers such as Photoshop will be wrong!

In fact, when you use the rotate functions of this utility, most of the image metadata (camera information, shot details, makernotes, etc.) are deleted. Therefore, I strongly recommend against using this program to rotate any of your digital photos.

I have also noticed that some images which were rotated that don't conform to 16x16 pixel multiples, the quantization tables don't appear to be rotated properly.

Because many new digital photographers may not be aware of this, Nikon even went so far as to issue a press release to warn of the potential dangers.

NOTE: The damage is done as soon as you press one of the rotate buttons . The disk icon  is just for copying the file and should not be thought of as a Save button!
The following table details some of the metadata corrupted / modified by Windows Picture and Fax Viewer: Removed Added Modified
IFD0-Orientation IFD0-x1001
IFD0-x1002

IFD0-xA401

IFD0-xA402

IFD0-xA403
  
SubIFD-ExifInteroperabilityOffset
SubIFD-CustomRendered

SubIFD-ExposureMode

SubIFD-WhiteBalance

SubIFD-SceneCaptureType
   SubIFD-MakerNote
SubIFD-UserComment
 
MakerNotes: Nearly all fields zeroed
out except: SerialNumber, ImageNumber
    

 

Auto-Rotation Utilities

There are several tools that allow the image content to be rotated losslessly in software, based on the information stored in the EXIF orientation flag. By far the best time to perform this is during image import (e.g. from memory card). Most import applications (such as DownloaderPro) can do this during the copy operation (from memory card to hard drive). Doing so ensure that all programs can see the image properly rotated, without having to rely on the EXIF Orientation flag. This means that even programs such as Microsoft's Windows Picture and Fax Viewer will also show correct orientation for portrait / vertical images.

Most programs will rotate the image content and then update the Orientation flag to reflect the new orientation (usually a value of 1), while still leaving other metadata intact.

 

读取图片文件的扩展信息(EXIF)
using System;
using System.Collections.Generic;
using System.Text;

namespace ExifWorks
{
//
// Utility class for working with EXIF data in images. Provides abstraction
// for most common data and generic utilities for work with all other.
//
//
// Copyright (c) Michal A. Valášek - Altair Communications, 2003-2005
// Copmany: http://software.altaircom.net, E-mail: [e-mail]
// Private: http://www.rider.cz, E-mail: [e-mail]
// This is free software licensed under GNU Lesser General Public License
//
//
// [altair] 10.09.2003 Created
// [altair] 12.06.2004 Added capability to write EXIF data
// [altair] 11.07.2004 Added option to change encoding
// [altair] 04.09.2005 Changed source of Width and Height properties from EXIF to image
// [altair] 05.09.2005 Code clean-up and minor changes
// [[e-mail]] 02-11-2006 C# translation
//
public class ExifManager : IDisposable
{

private System.Drawing.Bitmap _Image;
private System.Text.Encoding _Encoding = System.Text.Encoding.UTF8;

#region Type declarations

//
// Contains possible values of EXIF tag names (ID)
//
// See GdiPlusImaging.h
//
// [altair] 10.09.2003 Created
//

public enum TagNames : int
{
ExifIFD = 0x8769,
GpsIFD = 0x8825,
NewSubfileType = 0xFE,
SubfileType = 0xFF,
ImageWidth = 0x100,
ImageHeight = 0x101,
BitsPerSample = 0x102,
Compression = 0x103,
PhotometricInterp = 0x106,
ThreshHolding = 0x107,
CellWidth = 0x108,
CellHeight = 0x109,
FillOrder = 0x10A,
DocumentName = 0x10D,
ImageDescription = 0x10E,
EquipMake = 0x10F,
EquipModel = 0x110,
StripOffsets = 0x111,
orientation = 0x112,
SamplesPerPixel = 0x115,
RowsPerStrip = 0x116,
StripBytesCount = 0x117,
MinSampleValue = 0x118,
MaxSampleValue = 0x119,
XResolution = 0x11A,
YResolution = 0x11B,
PlanarConfig = 0x11C,
PageName = 0x11D,
XPosition = 0x11E,
YPosition = 0x11F,
FreeOffset = 0x120,
FreeByteCounts = 0x121,
GrayResponseUnit = 0x122,
GrayResponseCurve = 0x123,
T4Option = 0x124,
T6Option = 0x125,
ResolutionUnit = 0x128,
PageNumber = 0x129,
TransferFuncition = 0x12D,
SoftwareUsed = 0x131,
DateTime = 0x132,
Artist = 0x13B,
HostComputer = 0x13C,
Predictor = 0x13D,
WhitePoint = 0x13E,
PrimaryChromaticities = 0x13F,
ColorMap = 0x140,
HalftoneHints = 0x141,
TileWidth = 0x142,
TileLength = 0x143,
TileOffset = 0x144,
TileByteCounts = 0x145,
InkSet = 0x14C,
InkNames = 0x14D,
NumberOfInks = 0x14E,
DotRange = 0x150,
TargetPrinter = 0x151,
ExtraSamples = 0x152,
SampleFormat = 0x153,
SMinSampleValue = 0x154,
SMaxSampleValue = 0x155,
TransferRange = 0x156,
JPEGProc = 0x200,
JPEGInterFormat = 0x201,
JPEGInterLength = 0x202,
JPEGRestartInterval = 0x203,
JPEGLosslessPredictors = 0x205,
JPEGPointTransforms = 0x206,
JPEGQTables = 0x207,
JPEGDCTables = 0x208,
JPEGACTables = 0x209,
YCbCrCoefficients = 0x211,
YCbCrSubsampling = 0x212,
YCbCrPositioning = 0x213,
REFBlackWhite = 0x214,
ICCProfile = 0x8773,
Gamma = 0x301,
ICCProfileDescriptor = 0x302,
SRGBRenderingIntent = 0x303,
ImageTitle = 0x320,
Copyright = 0x8298,
ResolutionXUnit = 0x5001,
ResolutionYUnit = 0x5002,
ResolutionXLengthUnit = 0x5003,
ResolutionYLengthUnit = 0x5004,
PrintFlags = 0x5005,
PrintFlagsVersion = 0x5006,
PrintFlagsCrop = 0x5007,
PrintFlagsBleedWidth = 0x5008,
PrintFlagsBleedWidthScale = 0x5009,
HalftoneLPI = 0x500A,
HalftoneLPIUnit = 0x500B,
HalftoneDegree = 0x500C,
HalftoneShape = 0x500D,
HalftoneMisc = 0x500E,
HalftoneScreen = 0x500F,
JPEGQuality = 0x5010,
GridSize = 0x5011,
ThumbnailFormat = 0x5012,
ThumbnailWidth = 0x5013,
ThumbnailHeight = 0x5014,
ThumbnailColorDepth = 0x5015,
ThumbnailPlanes = 0x5016,
ThumbnailRawBytes = 0x5017,
ThumbnailSize = 0x5018,
ThumbnailCompressedSize = 0x5019,
ColorTransferFunction = 0x501A,
ThumbnailData = 0x501B,
ThumbnailImageWidth = 0x5020,
ThumbnailImageHeight = 0x502,
ThumbnailBitsPerSample = 0x5022,
ThumbnailCompression = 0x5023,
ThumbnailPhotometricInterp = 0x5024,
ThumbnailImageDescription = 0x5025,
ThumbnailEquipMake = 0x5026,
ThumbnailEquipModel = 0x5027,
ThumbnailStripOffsets = 0x5028,
ThumbnailOrientation = 0x5029,
ThumbnailSamplesPerPixel = 0x502A,
ThumbnailRowsPerStrip = 0x502B,
ThumbnailStripBytesCount = 0x502C,
ThumbnailResolutionX = 0x502D,
ThumbnailResolutionY = 0x502E,
ThumbnailPlanarConfig = 0x502F,
ThumbnailResolutionUnit = 0x5030,
ThumbnailTransferFunction = 0x5031,
ThumbnailSoftwareUsed = 0x5032,
ThumbnailDateTime = 0x5033,
ThumbnailArtist = 0x5034,
ThumbnailWhitePoint = 0x5035,
ThumbnailPrimaryChromaticities = 0x5036,
ThumbnailYCbCrCoefficients = 0x5037,
ThumbnailYCbCrSubsampling = 0x5038,
ThumbnailYCbCrPositioning = 0x5039,
ThumbnailRefBlackWhite = 0x503A,
ThumbnailCopyRight = 0x503B,
LuminanceTable = 0x5090,
ChrominanceTable = 0x5091,
FrameDelay = 0x5100,
LoopCount = 0x5101,
PixelUnit = 0x5110,
PixelPerUnitX = 0x5111,
PixelPerUnitY = 0x5112,
PaletteHistogram = 0x5113,
ExifExposureTime = 0x829A,
ExifFNumber = 0x829D,
ExifExposureProg = 0x8822,
ExifSpectralSense = 0x8824,
ExifISOSpeed = 0x8827,
ExifOECF = 0x8828,
ExifVer = 0x9000,
ExifDTOrig = 0x9003,
ExifDTDigitized = 0x9004,
ExifCompConfig = 0x9101,
ExifCompBPP = 0x9102,
ExifShutterSpeed = 0x9201,
ExifAperture = 0x9202,
ExifBrightness = 0x9203,
ExifExposureBias = 0x9204,
ExifMaxAperture = 0x9205,
ExifSubjectDist = 0x9206,
ExifMeteringMode = 0x9207,
ExifLightSource = 0x9208,
ExifFlash = 0x9209,
ExifFocalLength = 0x920A,
ExifMakerNote = 0x927C,
ExifUserComment = 0x9286,
ExifDTSubsec = 0x9290,
ExifDTOrigSS = 0x9291,
ExifDTDigSS = 0x9292,
ExifFPXVer = 0xA000,
ExifColorSpace = 0xA001,
ExifPixXDim = 0xA002,
ExifPixYDim = 0xA003,
ExifRelatedWav = 0xA004,
ExifInterop = 0xA005,
ExifFlashEnergy = 0xA20B,
ExifSpatialFR = 0xA20C,
ExifFocalXRes = 0xA20E,
ExifFocalYRes = 0xA20F,
ExifFocalResUnit = 0xA210,
ExifSubjectLoc = 0xA214,
ExifExposureIndex = 0xA215,
ExifSensingMethod = 0xA217,
ExifFileSource = 0xA300,
ExifSceneType = 0xA301,
ExifCfaPattern = 0xA302,
GpsVer = 0x0,
GpsLatitudeRef = 0x1,
GpsLatitude = 0x2,
GpsLongitudeRef = 0x3,
GpsLongitude = 0x4,
GpsAltitudeRef = 0x5,
GpsAltitude = 0x6,
GpsGpsTime = 0x7,
GpsGpsSatellites = 0x8,
GpsGpsStatus = 0x9,
GpsGpsMeasureMode = 0xA,
GpsGpsDop = 0xB,
GpsSpeedRef = 0xC,
GpsSpeed = 0xD,
GpsTrackRef = 0xE,
GpsTrack = 0xF,
GpsImgDirRef = 0x10,
GpsImgDir = 0x11,
GpsMapDatum = 0x12,
GpsDestLatRef = 0x13,
GpsDestLat = 0x14,
GpsDestLongRef = 0x15,
GpsDestLong = 0x16,
GpsDestBearRef = 0x17,
GpsDestBear = 0x18,
GpsDestDistRef = 0x19,
GpsDestDist = 0x1A
}

//
// Real position of 0th row and column of picture
//
//
//
// [altair] 10.09.2003 Created
//

public enum orientations
{
TopLeft = 1,
TopRight = 2,
BottomRight = 3,
BottomLeft = 4,
LeftTop = 5,
RightTop = 6,
RightBottom = 7,
LftBottom = 8
}

//
// Exposure programs
//
//
//
// [altair] 10.09.2003 Created
//

public enum ExposurePrograms
{
Manual = 1,
Normal = 2,
AperturePriority = 3,
ShutterPriority = 4,
Creative = 5,
Action = 6,
Portrait = 7,
Landscape = 8,
}

//
// Exposure metering modes
//
//
//
// [altair] 10.09.2003 Created
//

public enum ExposureMeteringModes
{
Unknown = 0,
Average = 1,
CenterWeightedAverage = 2,
Spot = 3,
MultiSpot = 4,
MultiSegment = 5,
Partial = 6,
Other = 255
}

//
// Flash activity modes
//
//
//
// [altair] 10.09.2003 Created
//

public enum FlashModes
{
NotFired = 0,
Fired = 1,
FiredButNoStrobeReturned = 5,
FiredAndStrobeReturned = 7,
}

//
// Possible light sources (white balance)
//
//
//
// [altair] 10.09.2003 Created
//

public enum LightSources
{
Unknown = 0,
Daylight = 1,
Fluorescent = 2,
Tungsten = 3,
Flash = 10,
StandardLightA = 17,
StandardLightB = 18,
StandardLightC = 19,
D55 = 20,
D65 = 21,
D75 = 22,
Other = 255
}

//
// EXIF data types
//
//
//
// [altair] 12.6.2004 Created
//
public enum ExifDataTypes : short
{
UnsignedByte = 1,
AsciiString = 2,
UnsignedShort = 3,
UnsignedLong = 4,
UnsignedRational = 5,
SignedByte = 6,
Undefined = 7,
SignedShort = 8,
SignedLong = 9,
SignedRational = 10,
SingleFloat = 11,
DoubleFloat = 12
}

//
// Represents rational which is type of some Exif properties
//
//
//
// [altair] 10.09.2003 Created
//
public struct Rational
{
public Int32 Numerator;
public Int32 Denominator;

//
// Converts rational to string representation
//
// Optional, default "/". String to be used as delimiter of components.
// String representation of the rational.
//
//
// [altair] 10.09.2003 Created
//

public override string ToString()
{
return ToString("/");
}

public string ToString(string Delimiter)
{
return Numerator + "/" + Denominator;
}

//
// Converts rational to double precision real number
//
// The rational as double precision real number.
//
//
// [altair] 10.09.2003 Created
//

public double ToDouble()
{
return (double)Numerator / Denominator;
}
}

#endregion

//
// Initializes new instance of this class.
//
// Bitmap to read exif information from
//
//
// [altair] 10.09.2003 Created
//
public ExifManager(System.Drawing.Bitmap Bitmap)
{
if (Bitmap == null)
throw new ArgumentNullException("Bitmap");
this._Image = Bitmap;
}

//
// Initializes new instance of this class.
//
// Name of file to be loaded
//
//
// [altair] 13.06.2004 Created
//
public ExifManager(string FileName)
{
this._Image = (System.Drawing.Bitmap)System.Drawing.Bitmap.FromFile(FileName);
}

//
// Get or set encoding used for string metadata
//
// Encoding used for string metadata
// Default encoding is UTF-8
//
// [altair] 11.07.2004 Created
// [altair] 05.09.2005 Changed from shared to instance member
//
public System.Text.Encoding Encoding
{
get
{
return this._Encoding;
}
set
{
if (value == null)
throw new ArgumentNullException();
this._Encoding = value;
}
}

//
// Returns copy of bitmap this instance is working on
//
//
//
//
// [altair] 13.06.2004 Created
//
public System.Drawing.Bitmap GetBitmap()
{
return (System.Drawing.Bitmap)this._Image.Clone();
}

//
// Returns all available data in formatted string form
//
//
//
//
// [altair] 10.09.2003 Created
//
public override string ToString()
{
System.Text.StringBuilder SB = new StringBuilder();

SB.Append("Image:");
SB.Append("\n\tDimensions: " + this.Width + " x " + this.Height + " px");
SB.Append("\n\tResolution: " + this.ResolutionX + " x " + this.ResolutionY + " dpi");
SB.Append("\n\tOrientation: " + Enum.GetName(typeof(Orientations), this.Orientation));
SB.Append("\n\tTitle: " + this.Title);
SB.Append("\n\tDescription: " + this.Description);
SB.Append("\n\tCopyright: " + this.Copyright);
SB.Append("\nEquipment:");
SB.Append("\n\tMaker: " + this.EquipmentMaker);
SB.Append("\n\tModel: " + this.EquipmentModel);
SB.Append("\n\tSoftware: " + this.Software);
SB.Append("\nDate and time:");
SB.Append("\n\tGeneral: " + this.DateTimeLastModified.ToString());
SB.Append("\n\tOriginal: " + this.DateTimeOriginal.ToString());
SB.Append("\n\tDigitized: " + this.DateTimeDigitized.ToString());
SB.Append("\nShooting conditions:");
SB.Append("\n\tExposure time: " + this.ExposureTime.ToString("N4") + " s");
SB.Append("\n\tExposure program: " + Enum.GetName(typeof(ExposurePrograms), this.ExposureProgram));
SB.Append("\n\tExposure mode: " + Enum.GetName(typeof(ExposureMeteringModes), this.ExposureMeteringMode));
SB.Append("\n\tAperture: F" + this.Aperture.ToString("N2"));
SB.Append("\n\tISO sensitivity: " + this.ISO);
SB.Append("\n\tSubject distance: " + this.SubjectDistance.ToString("N2") + " m");
SB.Append("\n\tFocal length: " + this.FocalLength);
SB.Append("\n\tFlash: " + Enum.GetName(typeof(FlashModes), this.FlashMode));
SB.Append("\n\tLight source (WB): " + Enum.GetName(typeof(LightSources), this.LightSource));
//SB.Replace("\n", vbCrLf);
//SB.Replace("\t", vbTab);
return SB.ToString();
}

#region Nicely formatted well-known properties

//
// Brand of equipment (EXIF EquipMake)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string EquipmentMaker
{
get
{
return this.GetPropertyString((int)TagNames.EquipMake);
}
}

//
// Model of equipment (EXIF EquipModel)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string EquipmentModel
{
get
{
return this.GetPropertyString((int)TagNames.EquipModel);
}
}

//
// Software used for processing (EXIF Software)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string Software
{
get
{
return this.GetPropertyString((int)TagNames.SoftwareUsed);
}
}

//
// orientation of image (position of row 0, column 0) (EXIF orientation)
//
//
//
//
// [altair] 10.09.2003 Created
//
public orientations orientation
{
get
{
Int32 X = this.GetPropertyInt16((int)TagNames.Orientation);

if (!Enum.IsDefined(typeof(Orientations), X))
return orientations.TopLeft;
else
return (Orientations)Enum.Parse(typeof(Orientations), Enum.GetName(typeof(Orientations), X));
}
}

//
// Time when image was last modified (EXIF DateTime).
//
//
//
//
// [altair] 10.09.2003 Created
//
public DateTime DateTimeLastModified
{
get
{
try
{
return DateTime.ParseExact(this.GetPropertyString((int)TagNames.DateTime), @"yyyy\:MM\:dd HH\:mm\:ss", null);
}
catch
{
return DateTime.MinValue;
}
}
set
{
try
{
this.SetPropertyString((int)TagNames.DateTime, value.ToString(@"yyyy\:MM\:dd HH\:mm\:ss"));
}
catch
{ }
}
}

//
// Time when image was taken (EXIF DateTimeOriginal).
//
//
//
//
// [altair] 10.09.2003 Created
//
public DateTime DateTimeOriginal
{
get
{
try
{
return DateTime.ParseExact(this.GetPropertyString((int)TagNames.ExifDTOrig), @"yyyy\:MM\:dd HH\:mm\:ss", null);
}
catch
{
return DateTime.MinValue;
}
}
set
{
try
{
this.SetPropertyString((int)TagNames.ExifDTOrig, value.ToString(@"yyyy\:MM\:dd HH\:mm\:ss"));
}
catch
{ }
}
}

//
// Time when image was digitized (EXIF DateTimeDigitized).
//
//
//
//
// [altair] 10.09.2003 Created
//
public DateTime DateTimeDigitized
{
get
{
try
{
return DateTime.ParseExact(this.GetPropertyString((int)TagNames.ExifDTDigitized), @"yyyy\:MM\:dd HH\:mm\:ss", null);
}
catch
{
return DateTime.MinValue;
}
}
set
{
try
{
this.SetPropertyString((int)TagNames.ExifDTDigitized, value.ToString(@"yyyy\:MM\:dd HH\:mm\:ss"));
}
catch
{ }
}
}

//
// Image width
//
//
//
//
// [altair] 10.09.2003 Created
// [altair] 04.09.2005 Changed output to Int32, load from image instead of EXIF
//
public Int32 Width
{
get { return this._Image.Width; }
}

//
// Image height
//
//
//
//
// [altair] 10.09.2003 Created
// [altair] 04.09.2005 Changed output to Int32, load from image instead of EXIF
//
public Int32 Height
{
get { return this._Image.Height; }
}

//
// X resolution in dpi (EXIF XResolution/ResolutionUnit)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double ResolutionX
{
get
{
double R = this.GetPropertyRational((int)TagNames.XResolution).ToDouble();

if (this.GetPropertyInt16((int)TagNames.ResolutionUnit) == 3)
{
// -- resolution is in points/cm
return R * 2.54;
}
else
{
// -- resolution is in points/inch
return R;
}
}
}

//
// Y resolution in dpi (EXIF YResolution/ResolutionUnit)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double ResolutionY
{
get
{
double R = this.GetPropertyRational((int)TagNames.YResolution).ToDouble();

if (this.GetPropertyInt16((int)TagNames.ResolutionUnit) == 3)
{
// -- resolution is in points/cm
return R * 2.54;
}
else
{
// -- resolution is in points/inch
return R;
}
}
}

//
// Image title (EXIF ImageTitle)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string Title
{
get
{
return this.GetPropertyString((int)TagNames.ImageTitle);
}
set
{
try
{
this.SetPropertyString((int)TagNames.ImageTitle, value);
}
catch { }
}
}

//
// User comment (EXIF UserComment)
//
//
//
//
// [altair] 13.06.2004 Created
//
public string UserComment
{
get
{
return this.GetPropertyString((int)TagNames.ExifUserComment);
}
set
{
try
{
this.SetPropertyString((int)TagNames.ExifUserComment, value);
}
catch { }
}
}

//
// Artist name (EXIF Artist)
//
//
//
//
// [altair] 13.06.2004 Created
//
public string Artist
{
get
{
return this.GetPropertyString((int)TagNames.Artist);
}
set
{
try
{
this.SetPropertyString((int)TagNames.Artist, value);
}
catch { }
}
}

//
// Image description (EXIF ImageDescription)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string Description
{
get
{
return this.GetPropertyString((int)TagNames.ImageDescription);
}
set
{
try
{
this.SetPropertyString((int)TagNames.ImageDescription, value);
}
catch { }
}
}

//
// Image copyright (EXIF Copyright)
//
//
//
//
// [altair] 10.09.2003 Created
//
public string Copyright
{
get
{
return this.GetPropertyString((int)TagNames.Copyright);
}
set
{
try
{
this.SetPropertyString((int)TagNames.Copyright, value);
}
catch { }
}
}

//
// Exposure time in seconds (EXIF ExifExposureTime/ExifShutterSpeed)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double ExposureTimeAbs
{
get
{
if (this.IsPropertyDefined((int)TagNames.ExifExposureTime))
// -- Exposure time is explicitly specified
return this.GetPropertyRational((int)TagNames.ExifExposureTime).ToDouble();
else
if (this.IsPropertyDefined((int)TagNames.ExifShutterSpeed))
//'-- Compute exposure time from shutter spee
return (1 / Math.Pow(2, this.GetPropertyRational((int)TagNames.ExifShutterSpeed).ToDouble()));
else
// -- Can't figure out
return 0;
}
}

public Rational ExposureTime
{
get
{
if (this.IsPropertyDefined((int)TagNames.ExifExposureTime))
// -- Exposure time is explicitly specified
return this.GetPropertyRational((int)TagNames.ExifExposureTime);
else
return new Rational();
}
}

//
// Aperture value as F number (EXIF ExifFNumber/ExifApertureValue)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double Aperture
{
get
{
if (this.IsPropertyDefined((int)TagNames.ExifFNumber))
return this.GetPropertyRational((int)TagNames.ExifFNumber).ToDouble();
else
if (this.IsPropertyDefined((int)TagNames.ExifAperture))
return Math.Pow(System.Math.Sqrt(2), this.GetPropertyRational((int)TagNames.ExifAperture).ToDouble());
else
return 0;
}
}

//
// Exposure program used (EXIF ExifExposureProg)
//
//
// If not specified, returns Normal (2)
//
// [altair] 10.09.2003 Created
//
public ExposurePrograms ExposureProgram
{
get
{
Int32 X = this.GetPropertyInt16((int)TagNames.ExifExposureProg);

if (Enum.IsDefined(typeof(ExposurePrograms), X))
return (ExposurePrograms)Enum.Parse(typeof(ExposurePrograms), Enum.GetName(typeof(ExposurePrograms), X));
else
return ExposurePrograms.Normal;
}
}

//
// ISO sensitivity
//
//
//
//
// [altair] 10.09.2003 Created
//
public Int16 ISO
{
get { return this.GetPropertyInt16((int)TagNames.ExifISOSpeed); }
}

//
// Subject distance in meters (EXIF SubjectDistance)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double SubjectDistance
{
get { return this.GetPropertyRational((int)TagNames.ExifSubjectDist).ToDouble(); }
}

//
// Exposure method metering mode used (EXIF MeteringMode)
//
//
// If not specified, returns Unknown (0)
//
// [altair] 10.09.2003 Created
//
public ExposureMeteringModes ExposureMeteringMode
{
get
{
Int32 X = this.GetPropertyInt16((int)TagNames.ExifMeteringMode);

if (Enum.IsDefined(typeof(ExposureMeteringModes), X))
return (ExposureMeteringModes)Enum.Parse(typeof(ExposureMeteringModes), Enum.GetName(typeof(ExposureMeteringModes), X));
else
return ExposureMeteringModes.Unknown;
}
}

//
// Focal length of lenses in mm (EXIF FocalLength)
//
//
//
//
// [altair] 10.09.2003 Created
//
public double FocalLength
{
get { return this.GetPropertyRational((int)TagNames.ExifFocalLength).ToDouble(); }
}

//
// Flash mode (EXIF Flash)
//
//
// If not present, value NotFired (0) is returned
//
// [altair] 10.09.2003 Created
//
public FlashModes FlashMode
{
get
{
Int32 X = this.GetPropertyInt16((int)TagNames.ExifFlash);

if (Enum.IsDefined(typeof(FlashModes), X))
return (FlashModes)Enum.Parse(typeof(FlashModes), Enum.GetName(typeof(FlashModes), X));
else
return FlashModes.NotFired;
}
}

//
// Light source / white balance (EXIF LightSource)
//
//
// If not specified, returns Unknown (0).
//
// [altair] 10.09.2003 Created
//
public LightSources LightSource
{
get
{
Int32 X = this.GetPropertyInt16((int)TagNames.ExifLightSource);

if (Enum.IsDefined(typeof(LightSources), X))
return (LightSources)Enum.Parse(typeof(LightSources), Enum.GetName(typeof(LightSources), X));
else
return LightSources.Unknown;
}
}

#endregion

#region Support methods for working with EXIF properties

//
// Checks if current image has specified certain property
//
//
// True if image has specified property, False otherwise.
//
//
// [altair] 10.09.2003 Created
//
public bool IsPropertyDefined(Int32 PID)
{
return (Array.IndexOf(this._Image.PropertyIdList, PID) > -1);
}

//
// Gets specified Int32 property
//
// Property ID
// Optional, default 0. Default value returned if property is not present.
// Value of property or DefaultValue if property is not present.
//
//
// [altair] 10.09.2003 Created
//
public Int32 GetPropertyInt32(Int32 PID)
{
return GetPropertyInt32(PID, 0);
}

public Int32 GetPropertyInt32(Int32 PID, Int32 DefaultValue)
{
if (IsPropertyDefined(PID))
return GetInt32(this._Image.GetPropertyItem(PID).Value);
else
return DefaultValue;
}

//
// Gets specified Int16 property
//
// Property ID
// Optional, default 0. Default value returned if property is not present.
// Value of property or DefaultValue if property is not present.
//
//
// [altair] 10.09.2003 Created
//
public Int16 GetPropertyInt16(Int32 PID)
{
return GetPropertyInt16(PID, 0);
}

public Int16 GetPropertyInt16(Int32 PID, Int16 DefaultValue)
{
if (IsPropertyDefined(PID))
return GetInt16(this._Image.GetPropertyItem(PID).Value);
else
return DefaultValue;
}

//
// Gets specified string property
//
// Property ID
// Optional, default String.Empty. Default value returned if property is not present.
//
// Value of property or DefaultValue if property is not present.
//
// [altair] 10.09.2003 Created
//
public string GetPropertyString(Int32 PID)
{
return GetPropertyString(PID, "");
}

public string GetPropertyString(Int32 PID, string DefaultValue)
{
if (IsPropertyDefined(PID))
return GetString(this._Image.GetPropertyItem(PID).Value);
else
return DefaultValue;
}

//
// Gets specified property in raw form
//
// Property ID
// Optional, default Nothing. Default value returned if property is not present.
//
// Is recommended to use typed methods (like etc.) instead, when possible.
//
// [altair] 05.09.2005 Created
//
public byte[] GetProperty(Int32 PID, byte[] DefaultValue)
{
if (IsPropertyDefined(PID))
return this._Image.GetPropertyItem(PID).Value;
else
return DefaultValue;
}

public byte[] GetProperty(Int32 PID)
{
return GetProperty(PID, null);
}

//
// Gets specified rational property
//
// Property ID
//
// Value of property or 0/1 if not present.
//
// [altair] 10.09.2003 Created
//
public Rational GetPropertyRational(Int32 PID)
{
if (IsPropertyDefined(PID))
return GetRational(this._Image.GetPropertyItem(PID).Value);
else
{
Rational R;
R.Numerator = 0;
R.Denominator = 1;
return R;
}
}

//
// Sets specified string property
//
// Property ID
// Value to be set
//
//
// [altair] 12.6.2004 Created
//
public void SetPropertyString(Int32 PID, string Value)
{
byte[] Data = this._Encoding.GetBytes(Value + '\0');
SetProperty(PID, Data, ExifDataTypes.AsciiString);
}

//
// Sets specified Int16 property
//
// Property ID
// Value to be set
//
//
// [altair] 12.6.2004 Created
//
public void SetPropertyInt16(Int32 PID, Int16 Value)
{
byte[] Data = new byte[2];
Data[0] = (byte)(Value & 0xFF);
Data[1] = (byte)((Value & 0xFF00) >> 8);
SetProperty(PID, Data, ExifDataTypes.SignedShort);
}

//
// Sets specified Int32 property
//
// Property ID
// Value to be set
//
//
// [altair] 13.06.2004 Created
//
public void SetPropertyInt32(Int32 PID, Int32 Value)
{
byte[] Data = new byte[4];
for (int I = 0; I < 4; I++)
{
Data[I] = (byte)(Value & 0xFF);
Value >>= 8;
}
SetProperty(PID, Data, ExifDataTypes.SignedLong);
}

//
// Sets specified property in raw form
//
// Property ID
// Raw data
// EXIF data type
// Is recommended to use typed methods (like etc.) instead, when possible.
//
// [altair] 12.6.2004 Created
//
public void SetProperty(Int32 PID, byte[] Data, ExifDataTypes Type)
{
System.Drawing.Imaging.PropertyItem P = this._Image.PropertyItems[0];
P.Id = PID;
P.Value = Data;
P.Type = (Int16)Type;
P.Len = Data.Length;
this._Image.SetPropertyItem(P);
}

//
// Reads Int32 from EXIF bytearray.
//
// EXIF bytearray to process
//
//
//
// [altair] 10.09.2003 Created
// [altair] 05.09.2005 Changed from public shared to private instance method
//
private Int32 GetInt32(byte[] B)
{
if (B.Length < 4)
throw new ArgumentException("Data too short (4 bytes expected)", "B");

return B[3] << 24 | B[2] << 16 | B[1] << 8 | B[0];
}

//
// Reads Int16 from EXIF bytearray.
//
// EXIF bytearray to process
//
//
//
// [altair] 10.09.2003 Created
// [altair] 05.09.2005 Changed from public shared to private instance method
//
private Int16 GetInt16(byte[] B)
{
if (B.Length < 2)
throw new ArgumentException("Data too short (2 bytes expected)", "B");

return (short)(B[1] << 8 | B[0]);
}

//
// Reads string from EXIF bytearray.
//
// EXIF bytearray to process
//
//
//
// [altair] 10.09.2003 Created
// [altair] 05.09.2005 Changed from public shared to private instance method
//
private string GetString(byte[] B)
{
string R = this._Encoding.GetString(B);
if (R.EndsWith("\0"))
R = R.Substring(0, R.Length - 1);
return R;
}

//
// Reads rational from EXIF bytearray.
//
// EXIF bytearray to process
//
//
//
// [altair] 10.09.2003 Created
// [altair] 05.09.2005 Changed from public shared to private instance method
//
private Rational GetRational(byte[] B)
{
Rational R = new Rational();
byte[] N = new byte[4];
byte[] D = new byte[4];
Array.Copy(B, 0, N, 0, 4);
Array.Copy(B, 4, D, 0, 4);
R.Denominator = this.GetInt32(D);
R.Numerator = this.GetInt32(N);
return R;
}

#endregion

#region " IDisposable implementation "

//
// Disposes unmanaged resources of this class
//
//
//
// [altair] 10.09.2003 Created
//
public void Dispose()
{
this._Image.Dispose();
}

#endregion

}

}

调用方法：
        ExifWorks.ExifManager exif = new ExifWorks.ExifManager(@"d:\2.jpg");
        System.Reflection.PropertyInfo[] ps = exif.GetType().GetProperties();
        StringBuilder sb = new StringBuilder();
        sb.Append("{");
        foreach (System.Reflection.PropertyInfo pi in ps)
        {
            try
            {
                object value = pi.GetValue(exif, null);
                sb.AppendFormat("\"{0}\":\"{1}\",", pi.Name, value.ToString()).Append("</br>");
            }
            catch (Exception)
            {

            }
        }
        sb.Append("}");
        Response.Write(sb.ToString());

 

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